Ready Made EHI is a Kotlin-based SDK that can provide you with an example template on how to integrate the GPS External Host Interface (EHI).

Ready Made EHI provides an example of a Mode 1 customer. This is where the customer provides the system of record, maintaining and holding the balance of each individual card. For more information about EHI Modes, see External Host Interface (EHI).

Within the SDK, there is example business logic on how balances of multiple cards can be be managed as an example to get you started.

SDK Use Cases

The SDK supports the following use cases:

Authorisation & Settlement flow

A regular transaction at a POS terminal. For example, a customer buying a book where they have sufficient balance to process the transaction correctly.

Authorisation & Reversal flow

A regular transaction where a reversal is issued before settlement. For example, a customer buying a book from a merchant where the merchant has already sold the stock and returns the money.

Final Presentment flow (Hard settlement)

An offline transaction where a card is scanned. For example, a customer traveling using Transport for London (TFL) where the fee is finalised offline, and applied at the end of the day.

Authorisation Request & Authorisation Advice flow

A transaction where the bank successfully authorises a transaction but the connection between the point of sale and the bank is broken. For example, a customer who tries to make a purchase with a sufficient balance, but the connection drops between their bank and the merchant resulting in a decline on the POS terminal.

Refund Authorisation & Refund Presentment Flow

A transaction that is accompanied by a refund at presentment. For example, a customer buys a laptop successfully, but the laptop breaks during warranty and as a result, the customer asks for a refund from the merchant.

Incremental Authorisation & Presentment Flow

A set of transactions that increment the amount authorised and presented on a card. For example, a customer stays in a hotel:

  • He checks in on Saturday morning, authorising the value of 200 GBP onto his card
  • He has dinner Saturday evening in the hotel bar, incrementally authorising the value of 50 GBP onto his card
  • He checks out Saturday, resulting in a partial presentment for the room of 150 GBP (Refunding the deposit)
  • Final presentment of 50 GBP for the meal

These uses cases are covered in more detail in the documents section of the SDK along with use case diagrams.

Accessing the Ready Made EHI SDK

You can download the SDK from [GPS Github Repository](www.link to git repo).
The readme file includes specific instructions on how to deploy the SDK, and further information is provided on the architecture within the documentation folder.

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Please Note

Hosting the SDK does not give you instant access to EHI. You need to contact your Implementation Manager to ensure the relevant card products are set up on GPS Apex.

Onboarding Process

Contact your Implementation Manager to request access to the Ready Made EHI SDK. Onboarding includes the following steps:

  1. Download the repository and host the SDK on your infrastructure.
  2. Contact your Implementation Manager to set up your test products on the GPS system.
  3. Test connectivity using the Card Transaction System (CTS).

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